Okay, wow. I have so much to say about this VN, yet at the same time, I struggle to come up with the right words. Still, I couldn't just say nothing, so if you'd allow me to ramble a bit...
(Spoiler warning)
So, I've noticed this VN was part of the Toxic Yuri VN jam. It's normally not my thing, personally, as I prefer romance stories where the drama doesn't revolve around on one or more of the love interests being abusive to each other, though I decided to give it a shot regardless once I heard about how the two protagonists differ on their views on fandom culture, and I'm glad I did. (Not that I have anything against people who enjoy toxic/dark romance, of course. Not every piece of fiction is for everyone and that's okay!)
Sunny and Anita remind me of anti-shipper and pro-shipper discourse, respectively. Like many other commenters here, I too relate to Anita, especially with the desire to create transgressive fiction while also worrying about seriously upsetting others and the fear of getting bullied by people on the Internet because of it. Sunny's perspective also mirrors the hypocrisy some Antis have. While they (almost always) aren't able to do the same things Sunny does, I have heard many horror stories about them sending shock material to pro-shippers. (Not that pro-shippers don't sometimes do the same thing to Antis, but y'know.)
I also wanted to note that despite this being a "toxic yuri" VN, it really isn't romantic at all. (In a good way, of course!) The relationship between Sunny and Anita is clearly one-sided. Anita, at best, is only friends with Sunny in a Stockholm syndrome-type way. (Until the end, at least.) I think the other comments go over Sunny's emotional and sexual abuse towards Anita much better than I can, but I'd also argue that Sunny isn't even in love with Anita, even if she probably can't see it herself. Sunny's only in love with the idealized version of Anita she crafted in her head, a fact Anita realizes towards the end when she sees herself as "Sunny's comfort character".
Don't know where to put this, but in the post-mortem, you mentioned that Sunny's POV was always in ADV mode to make Sunny's thoughts feel shallow and self-centered. I wouldn't have noticed that otherwise, but it's seriously a genius idea.
That's about all I have to say. Sunny was as insufferable as you intended her to be, and I can only hope that at some point after the ending, Anita can reignite her passion for her artistic work again, making the kind of work she really wants to make. Hopefully with at least one friend who appreciates Anita for who she is, including the part of herself that she kept hidden for so long.